The present invention is directed to soldered connections between hard material or hard metal parts and a steel support member. Hard metal tipped drilling, chipping and cutting tools have found wide acceptance, particularly for work on rock and construction materials. Accordingly, hard metal or hard material parts are used in the region of the drilling or chipping tip or cutting edge to increase the useful life of such tools and are distinguished by particularly low wear and the ability to work under high stresses. In producing such tools usually a support member formed of a more or less alloyed steel is provided with a recess in which a plate shaped hard metal or hard material part is inserted. The part inserted in the recess is secured by soldering.
Because of the different materials used in such tools, especially in the highly loaded region, there are special requirements for the material used for securing the hard metal parts to the support member. This is particularly significant, since the hard metal parts must project in the axial and/or radial direction beyond the support member of the drilling, chipping and cutting tools in the tip region. Though the hard metal parts are positively locked in the recesses of the support member, high and complex stresses involving compression, tension and shearing stresses develop at the connection during operation of the tool. The different thermal expansion characteristics of the connected parts cause additional high cooling stresses in the region of the soldered connection. As a result, the thermal expansion coefficient of the hard metal and the support member steel are in a ratio of approximately 1:3. Damage to the soldered connection can be avoided only if the solder, after the soldering process and during the cooling period is plastically deformable or ductile. Since high ductility means low strength, this characteristic is undesirable in actual practice.
As a result, there are special conditions which the solder used for connecting the hard metal with the support must meet. Accordingly, the solder must be ductile and capable of compensating for the different expansion behavior of the hard metal and the steel during the cooling process. At the same time, the solder must have a high strength, to counter the high dynamic stresses developed during the operation of the tool.